I'm going to say straight away that my methodology is flawed, but I will share what I have. Very many IPs in this range have hosted badness in the past year-and-a-bit (e.g. 5.133.179.165), mostly using subdomains.. to the extent that there are too many sites to analyse easily if I take the data from a passive DNS service.

Instead, I elected to use the DomainTools reverse DNS which limits the results to domains only (not subdomains) and these are mostly active sites. Running the list through my analyser checks that the IPs are valid, and would normally tell me things such as the Google Safebrowsing Diagnostics and SURBL rating.

Here's what is odd. None of the sites that I found [pastebin] have a negative reputation, I would expect to see about 1% in a normal sample, and out of 399 sites it comes back with zero. In fact, none of these sites seem to have any web presence at all, and all the ones that I have tried come back with almost no references on Google at all.

I am going to suggest that there is nothing of value in these IP ranges, and given that historically .SU domains have a bad reputation, then my suggestion is that you block traffic to: